Backwards compatible

Backward compatibility is a property of a system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in telecommunications and computing. Backward compatibility is sometimes abbreviated to BC, or called downward compatibility. Modifying a system in a way that does not allow backward compatibility is sometimes called "" backward compatibility. A complementary concept is forward compatibility, which is a design philosophy, usually based on open standards, that strives for methods that will continue to work with newer and future products. Design that is forward-compatible usually has a roadmap for compatibility with future standards and products.

The associated benefits of backward compatibility are the appeal to an existing user base through an inexpensive upgrade path as well as the network effect, which is particularly important, as it increases the value of goods and services proportionally to the size of the user base.

A good example is the Sony PlayStation 2 (PS2) which was backward compatible with games for its predecessor PlayStation (PSX or PSOne). While the PS2's selection of launch titles was small, sales of the console were nonetheless strong in 2000-2001 thanks to the large library of games for the preceding PSX/PSOne. This bought time for the PS2 to develop an installed base and developers to release more quality PS2 games for the crucial 2001 holiday season.

The associated costs of backward compatibility are a higher bill of materials if hardware is required to support the legacy systems; increased complexity of the product that may lead to longer time to market, technological hindrances, and slowing innovation; and increased expectations from users in terms of compatibility.

A good example is the Sony PlayStation 3, as the first PS3 iteration was expensive to manufacture in part due to including the Emotion Engine from the preceding PS2 in order to run PS2 games, since the PS3 architecture was completely different from the PS2. Subsequent PS3 hardware revisions have eliminated the Emotion Engine as it saved production costs while removing the ability to run PS2 titles, as Sony found out that backwards compatibility was not a major selling point for the PS3 in 2006-2009, in contrast to the PS2 in 2000-2001. The PS3's chief competitor, the Microsoft Xbox 360, took a different approach to backwards compatibility by using software emulation in order to run games from the first Xbox, rather than including legacy hardware from the original Xbox which was quite different than the Xbox 360, however Microsoft stopped releasing emulation profiles after 2007.

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